Sound and television receiver



Oct. 6, 1936. R, s, HOLMES 2,056,607

SOUND AND TELEVISION RECEIVER Filed June 28, 1934 5 sheets-sheet 1.STAT/@N 1. .STAT/0N Z.

Ralph Holmes T'T'RNEY 11000 ff. c. .9500 lf. c.

(LE) (LE) v Oct. 6, 1936. R. s.`HoLMEs 2,056,607

SOUND AND TELEVISION RECEIVER Filed June 28, 1954 5 Sheets-Sheet 2INVENTOR E I Ralph lHolme ATTORNEY 5 Sheets-Shea?I 3 Filed June 28, 1934INvLwron Ralph 5.1170111126 AT TOHNEX 5N DZsom.

#Allinll BY Oct. 6, 1936.

SOUND SIGNAL l.r S. HOLMES SOUND ANDl TELEVISION RECEIVER File'd June28, 1934 5 Sheets-Sheet 4 R. s. HOLMES SOUND AND TELEVISION RECEIVERFiled June 28, 1954 5 Sheets-Sheet 5 HLN NNN MKN QWNl

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ATTORNEY l Patented Oct. 6, 1936 PATENT OFFICE SOUND AND TELEVISIONRECEIVER Ralph S. Holmes, Haddonfield, N. J., assigner to' RadioCorporation of America. a corporation oi' Delaware Application .lune 28.1934, Serial No. 732,759

14 Claims.

My invention relates to radio receivers and particularly to receiversadapted to receive picture signals and sound signals simultaneously.

In Carlson Patent 1,975,059, issued September 25, 1934, there isdescribed a radio system in which picture signals and sound signals aretransmitted simultaneouslyfrom a transmitter in order that a pictureaccompanied by speech or music may be received. The picture signals andsound signals are transmitted on separate carrier waves which are spacedapart a denite fixed amount in the frequency spectrum. All thetransmitters in this system radiate two carrier waves, for the purposementioned, which are spaced apart the same definite fixed amount. Thedifferent transmitters transmit at different wave lengths, in accordancewith usual practice, to permit selection at a receiver of the desiredtransmitting station.

In a radio system of the above-described type, the receiver includes apicture translating device such as a cathode-ray tube and a soundtranslating device such as a loud speaker. It has been found that, intuning one of these receivers from one station to another, some veryunpleasant effects are encountered. One results from the sound channelof the receiver being tuned for an instant to the incoming picturesignal so as to produce a noise in the loud speaker. Another resultsfrom the picture channel of the receiverbeingtuned to the lncoming soundsignal for an instant so as to produce flashes of light on thefluorescent screen of the cathode-ray tube. Not only are these eectsdispleasing to a person operating the receiver, but they may result ininjury to the apparatus, especially the cathode-ray tube.

An object of my invention is to provide an improved receiver forreceiving picture and sound signals simultaneously.

More specifically, an object of my invention is to provide a receiverfor use in a system of the above-mentioned type in which the aforesaidundesirable effects are avoided.

A further object of my invention is to pro vide a picture and soundreceiver which will make a signal visible or audible only when thereceiver is tuned to two carrier waves.

In a preferred embodiment of my invention ll employ a superheterodynereceiver having an intermediate frequency channel through which picturesignals are supplied to a cathode-ray tube and having anotherintermediate frequency channel through which sound signals are sup--plied to a loud speaker. A noise suppressor circuit is provided whichnormally prevents signals from being impressed upon either thecathode-ray tube or the loud speaker. The noise suppressor circuit is soconnected to the intermediate frequency channels that, when signals ofthe proper amplitude appear in both channels, the suppressor isreleased.

In one embodiment of my invention I take vadvantage of the fact'that thefrequency spacing between the carriers of the intermediate frequencysignals is the same as the frequency spacing of the sound and picturecarrier waves sent out from a transmitter. The two intermediatefrequency carriers are heterodyned in a detector or mixer tube and theresulting beat frequency current is utilized to release the noisesuppressor. A

In another embodiment of my invention, instead of utilizing a beatfrequency, use is made of an automatic volume control or A. V. C.circuit in each intermediate frequency channel. Each A. V. C. circuit isso connected to a noise suppressor circuit that the suppressor will bereleased only when signals of sufiicient volume are being received inboth channels. I

Other objects, features and advantages of my invention will appear fromthe following description taken in connection with the accompanyingdrawings in which Figure l is a diagram showing the frequency spacing ofsignals transmitted in a system of the above-described type and alsoshowing certain selectivity characteristics of my improved receiver.

Fig. 2 is a diagram, similar to Fig. l, showing the frequency spacing ofa modified transmitting system,

Fig. 3 is a circuit diagram of an embodiment of my invention utilizingbeat frequency control,

Fig. Il is a circuit diagram of a modified form of the receiver shown inFig. 3,

Figs. 5 and 6 are circuit diagrams of embodiments of my inventionutilizing automatic volurne control circuits for actuating the noisesuppressor.

Referring to Fig. 1, two transmitter stations are indicated which areoperating on adjacent channels and which are widely spaced apartgeographically. Station No. 1 is represented as transmitting a picturesignal on a 50,000 k. c. carrier, the picture signal side bands having awidth of 1000 lr. c. This same station transmits sound signals on a51,500 k. o. carrier which may have a side band width of 10 k. c.

' Station No. 2, on an adjacent channel transmits a picture signal on a53,000 k. c. carrier and a sound'signal on a 54,500 k. c. carrier.

The curve I shows the selectivity characteristie of the picture channelin a receiver of the type described in the above-mentioned Carlsonpatent*'while the curve 3 shows the selectivity characteristic of theintermediate frequency sound channel in the same receiver. These curvesare positioned with respect to the diagram for station No. l to indicatethat the receiver is properly tuned to this station.

Consider now the operation of a receiver similar to the one shown in theCarlson patent, assuming the condition before the receiver was tuned-tostation No. 1: As the receiver is tuned towards stations No. 1 and No.2, the intermediate frequency sound channel will first receive thesignal from the picture carrier of 50,000 k. c. Under these conditionsno energy is being received by the intermediate frequency picturechannel, while the picture signal is appearing in the loud speaker as adisagreeable noise. Further tuning of the receiver tunes it accuratelyto station No. 1, as shown vin the diagram.

Assume now that the receiver is tuned towards station No. 2: It will beapparent that before the receiver is properly tuned, the sound channelwill receive the signal from the picture carrier of station No. 2 whilethe picture channel will be tuned to the sound carrier of station No. 1.As the signal from station No. 2 on the adjacent channel will be weakbecause of its geographic location, the picture signal noise in the loudspeaker may not be very disturbing. The sound signal from station No. 1,however, will be a strong signal and will appear on the fiuorescentscreen of the cathode-ray tube as flashes of light which are annoying toan observer and which may injure the tube.

With respect to the system indicated in Fig. 2, there is the samecondition of operation except that, because of the single side bandtransmis- `sion of the picture signals and the correspondlngly closerfrequency spacing of adjacent channels, the two intermediate frequencychannels of the receiver may supply signals to the loud speaker andcathode-ray tube only when the receiver is properly tuned to the pictureand sound signals from a single transmitting station.

Referring to the embodiment of my invention showing in Fig. 3, itcomprises a superheterodyne receiver having a radio frequency selectingcircuit 5, a first detector 1 and a tunable oscillator 9. As describedin the above-mentioned Carlson patent, the selecting circuit has a passrange wide enough to permit the passage of both the picture and soundsignals from a single transmitting station. At the same time theselectivity is sufficient to separate the signals from one transmittingstation from those from a different station. Preferably, the variablecondensers or other tuning elements of the selecting circuit and of theoscillator are connected to a Icommon control knob II to permitsimultanelplate current is flowing therethrough.

'intermediate frequency sound amplifier I 5 is tuned to 9,500 k. c. Theselecting circuits in both amplifiers are of the band-pass type, asindicated by the curves I and 3 in Figs. l and 2.

The output of the picture amplifier I3 is impressed upon an amplifiertube I1 which may be of the four-electrode type comprising a cathode I9,a control grid 2|, screen grid 23 and an anode 25. The signal appearingin the plate circuit of the tube |1 is impressed upon a second detector21 which may be of the diode type whereby the picture signal appearsacross a resistor 29 in the diode circuit.

It will be understood that the picture signal appearing across resistor29 includes the synchronizing impulses or signals. The picture signal isimpressed upon an amplifier 3| which includes circuits for separatingthe picture signal proper from the synchronizing signals. The output ofthe amplifier 3| is applied to the control grid 33 and to the deflectingdevices 34 and 35 of a cathode-ray receiver tube 36. The tubeillustrated is of the type having a first anode 31, a second anode 39and a fluorescent screen 4| at the end of the tube. y

The output of the sound amplifier I5 is im'- pressed upon an amplifiertube 43 which may be of the screen grid type comprising a cathode 45, acontrol grid 41, a screen grid 49 and an anode 5|. The sound signalappearing in the plate circuit of the amplifier tube 43 is impressedupon a second detector 53 which may be of the diode type whereby thesound signal appears across a resistor 55 in the diode circuit. Thesound signal is amplified by an amplifier 51 and supplied to a loudspeaker 59.

In accordance with my invention, the amplifier tubes 43 and I1 arenormally so biased that they will not amplify a signal. The circuitwhich maintains this high negative bias on the amplifier tubes comprisesa vacuum tube 6| having a cathode 63, a control grid 65, an anode 61 anda rectifier electrode 69. A tuned circuit 1|, which will be more fullydescribed hereinafter and which comprises an inductance coil 13 shuntedby a condenser 15, is connected at its upper terminal to the rectifierelectrode 69 while it is connected at its lower terminal through aresistor 11 to the cathode 63. The control grid 65 is connected to theend of the resistor 11 which is connected to the lower terminal of thetuned circuit 1|.

The cathode 63 of the tube 6| is connected through a resistor 19 toground while the anode 61 is connected to a suitable source of positivepotential whereby there is a flow of plate current through the resistor19 so long as the control grid 65 is not too negative with respect tothe cathode 63.

The cathodes of the amplifier tubes 43 and I1 are connected throughconductors 8| and 83 to the cathode end of the resistor 19 whereby theyare held positive with respect to ground when It will be seen,therefore,.that when no signal is being impressed upon the tuned circuit1I there is no ow of current through the diode circuit resistor 11, thecontrol grid 65 is at cathode potential and the flow of plate currentthrough the resistor 19 holds the cathodes 45 and I9 at a positivepotential with respect to ground.

By making the cathodes 45 and I9 of the amplifier tubes 43 and|1'positive with respect toA ground, the control grids 41 and 2| ofthese tubes are put at a negative potential with respect to theircathodes since they are connected to ground through their tuned inputcircuits. The circuit is so adjusted that when the grid 06 of the noisesuppressor tube- 0| is at cathode potential, the flow of plate currentthrough the resistor 19 makes the control grids of the amplifier tubes43 and I1 so negative that these tubes are ineective to amplify eitherpicture or sound signals. .l

The release of the suppressor is effected in response to signalsappearing in both the sound amplifier I5 and picture amplifier I3 bymeans of a mixer or detector tube 85 which comprises a cathode 81, acontrol grid 99, a second control grid 9|, a screen grid 93 and an anode95. The cathode 81 is connected to ground through a source of biasingpotential such as a. battery 91 whereby the control grids 89 and 9| arebiased to a suitable negative potential through the rey sistors 99 and|01, respectively;

' The control grid 89 is connected through a coupling condenser |03 anda conductor |05 to the output circuit of the sound amplifier I5 whilethe control grid 9| is connected through a coupling condenser |01 and aconductor |09 to the output circuit of the picture amplifier I3. Theanode 95 of the mixer tube is supplied with positive potential from asuitable source through a tuned circuit I I which is coupled to thetuned input circuit 1I of the noise suppressor tube 6|. The two coupledtuned circuits III and 1| form a circuit which is sharply tuned to 1500k. c.,

which is the beat frequency between the intermediate frequency picturesignal and the intermediate frequency sound signal.

When the receiver is so tuned to a station that signals appear in theoutput circuits of the sound and picture intermediate frequencyampliers, a beat frequency is produced in the tuned output circuit ofthe mixer tube 85 which frequency is selected by the tuned circuit andimpressed across the rectifier electrode 99 and the cathode 63. As a.result, current flows through the rectifier resistor 11 in such adirection as to make the control grid B5 negative with respect to thecathode 63. This flow of current through the resistor 11 is caused tohave a substantial steady value by shunting a filter condenser II3thereacross. If the picture and sound signals have a sufficientamplitude, the grid 65 of the suppressor tube is made so negative thatthe current flow through the plate resistor 19 is greatly reducedwhereby the high negative bias is removed from the control grids 2| and41 of the amplifier tubes I1 and 43 and these tubes function to amplifythe picture and sound signals so that they appear at the cathoderay tube36 and loud speaker 59, respectively.

From the foregoing description, it will be understood that if thepicture channel of the receiver is tuned to the sound signal or if thesound channel of the receiver is tuned to the picture signal, no signalwill be impressed upon either the cathode-ray tube or the loud speaker.With the transmitting system indicated in Fig. 1 there is a. possibleexception to this statement which would seldom occur in practice. If areceiver happens to be so located that it receives signals ofapproximately equal strength from two stations, such as stations No. 1and No. 2, which are on adjacent channels,' it is possible to getsignals on the cathode-ray tube and in the loud speaker by receiving asound signal from one station and a picture signal from the otherstation.

With the transmitting system indicated in Fig. 2, there is no conditionunder which signals will appear at the cathode-ray tube and loud speakerunless the receiver is properly tuned, since it must be tuned accuratelyto a station in order to obtain the 1500 k. c. beat note.

Under certain conditions either the sound signal or the picture signalarriving at a receiver from a transmitter may be weak or of poor qualitywhile the other signal from that transmitter is of good quality. Or, astation may transmit a picture signal unaccompanied by a sound signal orvice versa. Therefore, in order that a single signal may be receivedfrom a transmitter it is desirable that means be provided for making thesuppressor circuit of the receiver inoperative at will.

Referring to Fig. 3, this may be accomplished by `providing a switch 92in the plate circuit of the suppressor tube 8|. The receiver willnormally be operated with the switch 92 closed. If it is known that acertain station should be transmitting a program which may be either apicture or sound alone, the receiver will be tuned to that station whilethe switch 92 is closed. Then the switch 92 will be opened to permitreception of the single signal.

In a similar manner, the suppressor for the receiver shown in Fig. 6 maybe rendered ineffective by opening a switch 288 in the plate circuit ofthe suppressor tube 219.

In Fig. 4 there is shown a modification of the circuit shown in Fig. 3.In the two figures, like parts are indicated by the same referencenumerals. The difference between the two circuits is the manner in whichthe control or biasing voltageis supplied from the noise suppressor tube6I to the amplifier tubes 49 and I1.

In the modification shown in Fig. 4 the cathodes 45 and I9 of theamplifier tubes 43 and I1 are connected to ground while the controlgrids 41 and 2| are connected through conductors III and I|9 and througha filter resistor I2I to a biasing resistor |23 in thenoise suppressorcircuit. The bias resistor |23 is included in the plate circuit of thenoise suppressor tube 6| in series with the secondary |25 of atransformer |21 which supplies voltage to the plate 61. It will beunderstood that a battery may be substituted in the plate circuit forthe alternating current supply if desired. It will be seen that whenplate current iows through the biasing resistor |23, the control grids41 and 2| of the amplifier tubes 43 and I1 are biased negatively withrespect to their cathodes. When the plate of the noise suppressor tube6I is supplied from an alternating current source as shown, it ispreferred to connect a lter condenser |29 be# tween one end of thefilter resistor |23 and ground in order to supply a substantiallyconstant bias voltage to the amplifier tubes 43 and I1.

The operation of the circuit is substantially the same as that of thecircuit shown in Fig. 3. If one of the intermediate frequency amplifierchannels is not receiving signal energy, no beat note appears in theoutput circuit of the mixer tube 85 and the flow of current through thebiasing resistor |23 maintains the amplifier tubes 43 and I1 biased sonegatively that neither one of them will amplify a signal impressed uponit. n the other hand, when both intermediate frequency channels arereceiving energy, a. 1500 k. c. beat note appears in the output circuitof the mixer tube and the flow of current 'amplifier tubes through thebiasing resistor I 23 is reducedto a value which permits the twoamplifier tubes 43 and |1 to amplify the signals impressed upon them.

Referring to Fig. 5, there is shown an embodiment of my invention inwhich a noise suppressor circuit is controlled by means of automaticvolume control circuits. The radio frequency amplifier or selectingcircuit, the first detector, and the oscillator superheterodyne receiverare indicated at |3|. The output circuit of the first detector iscoupled to the input circuit of an intermediate frequency sound ampliner33 through a secondary winding |35 of a transformer |31 and to theintermediate frequency picture amplifier |39 through another secondaryWinding |4| of the transformer |31.

In order to simplify the drawings, only the circuit of the first tubeineach intermediate frequency amplifier is shown. The input circuit of thefirst tube |43 of the sound amplifier |33 includes the secondary winding|35 which is tuned to the sound intermediate frequency by a condenser|45. The cathode |41 of the tube |43 is maintained at a positivepotential with respect to ground by means of a self biasing resistor |49which is shunted by the usual bypass condenser |5I.

The gain of the amplifier tube |43, as well as the gain of otherintermediate frequency amplifier tubes (not shown), is controlledautomatlcally by varying the bias on its control grid |53 through aconductor |54 to the output circuit of an automatic volume control tube|55.

The output circuit of the sound amplifier |33 is coupled through a tunedintermediate frequency transformer |51 to an amplifier tube |59, whichin turn has its output circuit coupled to a second detector |6|. Theamplifier tube |59 may be of the screen grid type having its cathode |63maintained at a positive potential with respect to ground by means of aself-bias resistor |65 and having its control grid |61 connected throughvthe secondary of the transformer |51 and through a conductor |59 to thenoise suppressor circuit which will be described later. In theparticular embodiment illustrated, the second detector ISI is of thediode type and includes in its circuit a resistor |1| across which thesound signals appear.

The picture amplifier |39 is similar to the sound amplifier and includesa first amplifier tube |13 which has its cathode |15 maintained at apositive potential with respect to ground by means of a self-biasresistor |11. The control grid |19 of this amplifiertube, as well as thecontrol grids of other intermediate frequency (not shown), is connectedthrough a conductor |8| to the output circuit of an automatic volumecontrol tube |83.

The output circuit of the picture amplifier |39 is coupled through atuned intermediate frequency transformer |85 to an amplifier tube |81which has its output circuit coupled to a second detector |89. As in thesound channel, the second detector |89 may be of the diode type having aresistor |9| in its circuit across which the picture signals appear.

Referring now to the automatic volume control circuit for the soundchannel, it comprises the amplifier tube |55 which may be of the screengrid type having a cathode |93, a control grid |95, a screen grid |91and an anode |99. The tube |55 also includes a rectifier electrode 20|which is positioned adjacent to a small section of the cathode |93. Thecathode |93 is held positive with respect to ground by means of aself-biasing resistor 203 which is shunted by a suitable by-passcondenser 205.

The control grid |95 is connected through a resistor 201 to a point onthe self-biasing resistor 203 for maintaining the tube |55 biased atsuch a value that it will function efliciently as an amplifier. Theupper portion of the selfbiasing resistor 203 is preferably shunted byanother by-pass condenser 209. The plate |99 and the screen grid |91 aresupplied with positive potentials from any suitable source.

The input circuit of the tube |55 is coupled through a couplingcondenser 2|| to the` output circuit of the sound amplifier |33.Therefore, when an incoming signal is received, an amplified highfrequency current appears in the plate circuit of the amplifier tube|55. This current is impressed upon the rectifier section of the tube|55 through a sharply tuned transformer 2|3. The rectifier circuit,which includes a resistor 2|5, may be traced from the rectifier plate20| through the secondary 2|1 of the transformer 2|3 and the resistor2|5 to ground and through ground and the self-biasing resistor 203 tothe cathode |93. v

It will be seen that as soon as a sound signal appears in the output ofthe sound amplifier |33,

current is caused to fiow through the rectifier circuit in such adirection as to make the upper end of the resistor 2|5 negative withrespect to ground. It is to this end of the resistor 2|5 that theconductor |54 from the control electrodes of the intermediate frequencyamplifier tubes is connected. The connection is made through a filterresistor 2|9 which has filter condenser 22| connected between one endand ground. A filter condenser 223 is also connected across the resistor2|5. It will be understood that as the strength of the signal increasesthe upper end of the resistor becomes more negative, whereby a morenegative bias is applied to the amplifier tube |43 to reduce the gain.

The A. V. C. circuit for the picture channel is the same as the A. V. C.circuit described above and includes the amplifier tube |83 which hasits input circuit coupled to the output'circuit of the picture amplifier|39 through a coupling condenser 225 and its output circuit coupledthrough a sharply tuned transformer 221 to a rectifier section of. thetube. The circuit of the rectifier section includes a resistor 229 whichis so connected that its upper end becomes increasingly negative as thestrength of the picture signal increases. The conductor |8| from thecontrol grids of the intermediate frequency amplifier tubes is connectedthrough a filter resistor 23| to the upper end of the resistor 229.

In accordance with my invention, the sound channel is provided with anoise suppressor tube 233 while the picture channel is provided with anoise suppressor tube 235. 'I'he noise suppressor tubes may be of thescreen grid type. The tube 233 comprises a cathode 231, a control grid239, a screen grid 24|, and a plate 243. The control grid 239 isconnected through a filter resistor 245 to the upper end of the volumecontrol resistor 2|5. The cathode 231 may be connected to ground througha battery 241 or another source of biasing potential for maintaining thecathode negative with respect to ground for providing the desired delayin the noise suppressor action. A filter condenser 249 is connectedbetween the grid end of the filter resistor 245 and ground.

Since the bias voltage supplied by the battery 241 opposes the voltagedrop across the volume control resi'stor 2|5, the control grid 239 willnot become negative until the amplitude of the incoming signal reaches apredetermined value. Until the control grid 239 reaches a certainnegative value, current flows through a resistor 250 in the platecircuit of the tube 233, the plate potential being supplied through atransformer 25| or a battery (not shown). So long as plate current flowsthrough the resistor 250, its upper end is negative with respect toground.

The control grid |61 of the amplifier tube |59 is connected through theconductor |69 and through a filter resistor 253 to the upper end of theplate resistor 259 whereby the amplifier tube |59 is biasedsubstantially to cut-oir until the amplitude of an incoming signalreaches a value sufficient to put a high negative bias on the controlgrid of the noise suppressor tube 293. 'I'he usual filter condenser 255is connected between the grid end of the filter resistor 253 and ground.

In the picture channel, the noise suppressor circuit is the same as.that in the sound channel. The input circuit of the tube 235 isconnected across the volumel control resistor 229 whereby the tube 235is biased approximately to cut-a when an incoming signal reaches apredetermined amplitude. Until the signal reaches this amplitude,current flows in the plate circuit of the tube 235 through the plateresistor 250 which is common to the plate circuits of both suppressortubes. Likewise, both plate circuits are supplied with plate voltagefrom the same alternating current source.

The control grid of the amplifier tube |81 is connected through thesecondary of transformer |85 and through a conductor 251 to the grid endof the filter resistor 253, whereby the tube |81 is rendered ineffectiveto amplify a signal while there is a flow oi plate current through theresistor 259.

The suppressor circuit is so adjusted that if the resistor 259 has platecurrent flowing therethrough from either the suppressor tube 233 or thesuppressor tube 235, both amplier tube |59 and amplifier tube |81 willbe biased so negatively that they are ineffective to amplify a signal.Therefore, if only one of the signal channels is receiving a signal, thenoise suppressor of the other channel is preventing a signal from beingapplied to either the loud speaker or to the cathode-ray tube. Forexample, if the sound channel is tuned to the picture signal the picturesignal will not appear as noise in the loud speaker because the noisesuppressor circuit in the picture channel will be holding the amplifiertube in the sound channel negatively biased to a high value.

The suppressor tubes 233 and 235 should hav their voltages adjusted togive quicker cut-or than the intermediate frequency amplifier 'tubeswhich are controlled directly from the A. V. C. circuit. It has beenfound that RCA-57 type tubes are satisfactory as suppressor tubes whenRCA-58 type tubes are being used as the intermediate frequency ampliertubes.

In order to insure that the receiver will be tuned exactly to a desiredstation before the noise suppressor releases, the transformers 213 and221 may be tuned to have an over-al1 selectivity (together with .thepreceding tuned transformers) shown by the curves 259 and 258,respectively, in Figs. 1 and 2. In some cases it may be preferred totune the transformers 2|3 and 221 no more sharply than each of thepreceding intermediate frequency transformers. It will be seen, however,that in any case the selec- .tivity of the sound channel insures thatthe picture channels will be tuned with reasonable accuracy to thepicture signal .before the noise suppressor releases.

In Fig. 6, I have shown a simplified form of noisesuppressor circuit inwhich the A. V. C. action is utilized. In Figs. 5 and 6 like parts areindicated by the same reference numerals. In this modification, thesecond detectors |6| and |89 are coupled directly to the output circuitsof the amplifiers |33 and |39, respectively, and the A. VT. C. bias forthe intermediate frequency amplifier tubes is obtained from the resistorin the diode circuit.

Sound signals appearing across the resistor 1| in the circuit of thediode i6| are supplied through a coupling condenser 259 to the inputcircuit of an audio frequency amplifier tube 26|. The tube may be of thethree electrode type comprising a cathode 263, a control grid 265, and aplate 261.

In the picture channel, the picture signals appearing across theresistor |9| in the second detector circuit are supplied through acoupling condenser 289 to a picture amplifier tube 21| which may be ofthe three electrode type comprising a cathode 213, a control grid 215,and a plate 211. f

Signals are prevented from appearing at the loud speaker and cathode-raytube by biasing the 4grids of the sound amplifier tube 26| and thepicture ampller tube 21| to a high negative value. This is accomplishedby means of a circuit comprising a suppressor tube 219 which functionsas two separate amplifier tubes. It includes one set of electrodesconsisting of a cathode 28|, a control grid 283, and a plate 285, and asecond set of electrodes consisting of a cathode 291, a control grid 289and a plate 29|. The cathodes 281 and 291 are connected to ground whilethe anodes 285 and 29| are connected together and supplied through a.transformer 293 with potential from an alternating current source orfrom a direct current source (not shown). The plate circuit of the tube219 includes a resistor 295 for supplying the control bias to the audioamplifier tube 26E and picture amplier tube 21i.

The control electrode 289 of the tube 219 is connected through a lterresistor 291 tothat end of the second detector resistor |1| whichsupplies the A. V. C. bias for the tubes in arnplifier 999. The othercontrol grid. 283 of the tube 219 is connected through a filter resistor299 to that end of the second detector resistor 191 lwhich supplies A.V. C. bias for the tubes in amplifier 139. It will be seen that if thereis no signal in one of the signal channels, one of the control grids ofthe suppressor tube 219 will be substantially at ground potentialwhereby there will be a flow of plate current through the plate resistor295 to so bias the amplifier tubes 251 and 2li that they are ineffectiveto amplify a signal. On the other hand, if the receiver is properlytuned to a station, the sound signal will cause a high negative bias tobe put on the control grid 299 of the noise suppressory tube 219 whilethe picture signal will cause a high negative bias to be put on theother control grid 283 of the noise suppressor tube 219 and the'iiow ofcurrent through the plate resistor vso 295 will be so reduced in valuethat the amplifier tubes 28| and 21| will be properly biased foramplifying the sound and picture signals.

From the foregoing description it will be un.- derstocd that by applyingmy invention to a combined television and sound receiver, the receiveris made inoperative when either the television carrier wave or the soundcarrier wave is not being received or when either one of them is soreduced in value that the reception would not be satisfactory. Thereceiver is operative to render a signal visible or audible only whenthe receiver is properly tuned to two carrier waves having apredetermined frequency spac- Various other modifications may be made inmy invention without departing from the spirit and scope thereof and Idesire, therefore, that only such limitations shall be placed thereon asare necessitated by the prior art and are set forth in the appendedclaims.

I claim as my invention:

1. In a radio receiver for the simultaneous reception of two carrierwaves, each of which is modulated by a different signal, two translatingdevices, and means responsive only to the reception of both of saidcarrier waves for impressing one of said signals upon one of saidtranslating devices.

2. A receiver according to claim 1 characterized in that one of saidtranslating devices is a loud speaker and the other translating device acathode-ray tube.

3. In a radio receiver for receiving simultaneously two modulatedcarrier waves having a predetermined frequency spacing, a tunableselecting circuit, two translating devices, means for demodulating saidcarrier waves whereby two signals are produced, circuit connectionsbetween said demodulating devices and said translating devices wherebyone of said signals mayA be impressed upon one of said translatingdevices and the other of said signals may be impressed upon the other ofsaid translating devices, and means responsive only to the reception ofboth of said carrier waves for impressing one of said` signals upon oneof said translating devices.

4. In a receiver for receiving simultaneously one carrier wave modulatedby a picture signal and another carrier wave modulated by a soundsignal, a tunable selecting circuit,`a.cathoderay tube, a loud speaker,means for demodulating said carrier waves to produce a picture signaland a sound signal, means whereby said picture signal and said soundsignal may be impressed upon said cathode-ray tube and loud speaker,respectively and means responsive only to the reception of both of saidcarrier waves for impressing one of said signals upon said loud speaker.

5. A radio receiver comprising a radio frequency selecting circuitadapted to select a. plurality of modulated carrier waves, means forheterodyning said carrier waves to a plurality of intermediate frequencysignals, means for demodulating one of said intermediate frequencysignals to produce a certain signal, means for impressing said certainsignal upon a translating device, means for demodulating another of saidintermediate frequency signals to produce a different signal, means forimpressing said diiIerent signal upon a second translating device, andmeans for preventing either saidcertain signal or said different signalfrom being impressed upon said translating devices so long as saidselecting circuit is not tuned to a plurality of said carrier waves.

6. A receiver according to claim 5 characterized in that means isprovided for making said last means ineffective at the will of theoperator.

7. In a receiver for the simultaneous reception of two carrier waves,each of which is modulated by a signal, a plurality of translatingdevices. means for heterodyning one of said carrier waves with the otherof said carrier waves to produce a beat frequency, and means responsiveto the production of said beat frequency I for impressing said signalsupon said translating devic.

8. A receiver according to claim 7 characterized in that one of saidtranslating devices is a cathode-ray tube for the reception of picturesignals.

9. In a receiver for the simultaneous reception of two carrier waves, atleast one of which is modulated by a signal, means for heterodyning saidcarrier waves to two intermediate frequency signals. means forheterodyning one of said intermediate frequency signals by the other ofsaid intermediate frequency signals to produce a beat frequency, atranslating device, and means for impressing said signal upon saidtranslating device in response to the production of said beat frequency.

10. A receiver according to claim 9 characterized 'in that said signalis supplied to said translating device through an amplifier, and furthercharacterized in that said last means includes means for maintainingsaid amplifier substantially ineffective to amplify so long as said beatfrequency is not being produced.

11. In a receiver for the reception of at least two carrier waves, eachmodulated by a signal, means for selecting said carrier waves, means forconverting said modulatedvcarrier waves to intermediate frequencysignals, an amplifier tuned to one of said intermediate frequencysignals, an amplifier tuned to another of said intermediate frequencysignals, a plurality of translating devices, means for transferringsignal energy from one of said amplifiers to one of said translatingdevices, means for transferring signal energy from said second amplifierto another of said translating devices, and means for making said twolast-named means ineffective in response to the signal strength ineither, of'said amplifiers falling below a predetermined value.

l2. A receiver according to claim 11 characterized in that one of saidamplifiers is tuned comparatively sharply to receive sound signals whilethe second of said amplifiers is tuned comparatively broadly to receivepicture signals, and further characterized in that said one translatingdevice is a loud speaker while said. second translating device is acathode-ray tube.

13. A receiver comprising a broadly tuned radio frequency selectingcircuit, a heterodyne oscillator and detector, a sharply tunedintermediate frequency amplifier, a broadly tuned intermediate frequencyampliiier, an automatic volume control operating in conjunction witheach intermediate amplifier in such a manner that the output of eachamplifier remains substantially constant under proper receivingconditions, and means controlled by both automatic volume controls forrendering a subsequent amplifier tube in each channel inoperative when asignal of insufiicient strength to operate the automatic monaco? volumecontrols is impressed upon either intermediate amplifier.

14. A receiver comprising a broadly tuned radio frequency selectingcircuit, a heterodyne oscillator and detector, a sharply tunedintermediate frequency amplifier, an automatic volume control operatingin conjunction with said intermediate frequency amplier to maintain itsoutput substantially constant when a'signal of sutilcient intensity isbeing received, a second intermediate frequency amplier having arelatively broad selectivity characteristic tuned to a slightly dfferentfrequency than the first intermediate amplier, an automatic volumecontrol operating in conjunction with the second' intermediate frequencyamplifier to maintain its output substantially constant when a signal o!sumcient intensity is being received, said second automatic volumecontrol having a selectivity characteristic such that it will operateover only a substantially small band of the frequenciesv passed by thesecond intermediate amplifier, a demodulating device following eachintermediate amplifier, an amplifier following each demodulator, autilization device folowing each of the last mentioned apliers, andmeans responsive to the outputs of both automatic volume controls forpreventing any signal voltage from reaching either utilization devicewhen a signal of insufficient strength or of improper frequency tooperate the automatic volume controls is impressed upon eitherintermediate frequency amplifier.

RALPH S. HOLMES.

